Center for Marine Acoustics Recent Work

Characterizing HRG Sound Sources

High-resolution geophysical (HRG) sound sources are used in activities concerning all BOEM program areas and they require consistent, well-grounded regulation. BOEM and the National Marine Fisheries Service (NMFS) both regulate these activities, and there is room for improving regulatory regimes. For example, NMFS has required MMPA authorization for some sound source types but not others. Additional research and analyses are warranted to determine whether authorizations should be required and whether mitigation measures are appropriate, considering the risk that surveys may pose to marine life. Improved clarity on such authorizations and mitigations and a more transparent and firmer basis in science and law will be a boon to many stakeholders whose programs and interests concern the affected activities. The federal agencies involved in ocean resource mapping and use have a particular stake and include (in addition to BOEM) the U.S. Geological Survey (USGS), the National Science Foundation (NSF), the U.S. Navy and the National Oceanic and Atmospheric Administration (NOAA).

The CMA has taken the lead to tackle this problem, developing the necessary technical information and facilitating discussions across agencies through a three-pronged approach:

• SOLUTION: Measuring commonly used HRG sound sources. Historically, HRG sound sources have not been well-calibrated, making it difficult to assess and compare their potential impact on marine species. The CMA, together with the USGS, has addressed this shortfall with a study measuring HRG sources in both the lab and the field and comparing sound propagation with model predictions.
   
• SOLUTION: Developing a baseline sound source list. The CMA is developing and refining a guide for federal agencies to classify and understand the physical qualities of anthropogenic sound sources. This includes sources that produce sound on command (e.g., airguns, side-scan sonars, sub-bottom profilers) as well as sources that produce sounds incidentally (e.g., dredges, drilling platforms, vessels). This guide provides federal agencies with a common classification and description for these sources.
   
• SOLUTION: Advancing scientific rationale for sound source classification. BOEM worked with USGS and NSF to complete a technical analysis of active acoustic sources (including both seismic airguns and high resolution geophysical sources). The paper divides the sources into four tiers based on their physical characteristics and their potential to affect marine species. Seismic airguns are broken into two tiers based on their size. HRG sources fall into two tiers: Tier 3 sources may not result in incidental take if certain mitigations are applied, while Tier 4 sources are considered to be de minimis, meaning they are unlikely to result in incidental take of marine mammals even without any mitigation. One major contribution of the paper is the description of several key physical factors that should be used when analyzing any sound source (e.g., beamwidth, duty cycle, radiated power, etc.).

Although the technical analysis has recently been published, we are still working with our partners at the National Marine Fisheries Service to determine how these sources will be regulated moving forward. We expect the outcome of this work will help guide BOEM and NMFS staff in determining which sound sources will require an Incidental Harassment Authorization (IHA) and which will not.

Innovative Risk Assessment Frameworks

Before BOEM authorizes offshore activities, the bureau and industry applicants must assess the potential risk of acoustic impacts to marine species. Typically, complex acoustic propagation models and animal movement models are combined to generate a predicted number of “takes” under the ESA, MMPA or both. These estimates tend to produce very high take numbers because the assumption for calculations is highly conservative by design, and they do not incorporate other relevant information (e.g., life history, species status, and behavioral context), which is essential for realistically assessing actual impacts on population sustainability.

SOLUTION: Develop a customized, quantifiable risk assessment framework for noise-producing activities addressing biologically significant factors and cumulative effects of multiple overlapping activities and other stressors. The CMA supported the development of a customized, quantifiable risk assessment framework for reviewing the noise-producing activities (e.g., seismic surveys and pile driving) that BOEM authorizes and providing risk assessments for species and populations. This new framework integrates relevant information about species vulnerability (e.g., population size, habitat use) and other stressors (e.g., chronic noise, other environmental conditions) to provide an overall assessment of risk when a species is exposed to particular sound sources. The framework also considers the aggregate impacts of multiple overlapping activities, such as the concurrent construction of multiple offshore wind farm facilities. The result is clearer identification of higher risk areas where regulatory attention should be focused. It is a holistic assessment of risk that is not based on simple take numbers and is much more informative to decision-making.

Guidelines for Acoustic Modeling and Sound Field Measurements for Pile-Driving

ACOUSTIC MODELING: All offshore wind Construction and Operation Plans (COPs) must include a section on acoustic modeling designed to predict the number of marine mammal “exposures” that could occur during pile-driving operations. Historically, third-party contractors have supplied most of the COPs’ acoustic modeling. This has led to inconsistent report quality and created confusion for BOEM reviewers.

SOLUTION: Develop standard third-party modeling guidelines. The CMA worked with BOEM’s renewable energy experts to develop modeling guidelines to provide offshore wind operators a list of minimum requirements for the acoustic models that should be included in a COP. Using these guidelines, BOEM will receive acoustic modeling with similar details and organizational structure, which will save time and ensure consistency across projects.

SOUND FIELD MEASUREMENTS: It is also important for operators to measure the radiated sound field during pile-driving, to ensure that the received levels at particular distances match what was modeled. These measurements allow regulators to determine the adequacy of certain mitigation and monitoring procedures.

SOLUTION: Provide a list of minimum requirements for sound field measurements. Together with BOEM’s renewable energy experts, the CMA produced guidance on the type of measurements that shall be conducted during pile-driving. Given the complexity of the marine environment, it is nearly impossible to provide universal direction that would cover every possible scenario; this document provides a list of minimum requirements to begin to fill the need.

Quantitative Assessment of Ocean Soundscapes

Soundscapes are all the sounds - natural and anthropogenic - that exist in an environment, considered as a whole. Scientists know little about the ocean soundscapes in some geographic areas; even where studies have been conducted, human contributions to marine soundscapes cover a range of frequencies and geographic scales that make them challenging for scientists to quantify. The study of soundscapes is a relatively new field in marine acoustics, but it is important to deepen our understanding of marine soundscapes so we can better understand potential impacts of anthropogenic activity. Patterns in ocean soundscapes that occur over certain geographic areas or periods of time can be indicative of important biological activities like whale migration or fish spawning and may reveal previously unknown biological patterns. More complete information on ocean soundscapes will help BOEM and others assess the impact of noise from activities they authorize or generate.

SOLUTION: Identify and fund key projects to address soundscape needs. Working with BOEM’s regional and environmental studies experts, the bureau funded two key projects that address ocean soundscape needs.

• ADEON Project – The Atlantic Deepwater Ecosystem Observatory Network (ADEON) project used a series of moorings in the Atlantic to measure acoustic, physical and biological conditions to elucidate trends and contributions to Atlantic soundscapes.
• Passive Acoustic Monitoring Program for the Northern Gulf of Mexico – Similar to the ADEON project, the Passive Acoustic Monitoring (PAM) Program for the Northern Gulf of Mexico collected and analyzed data near the Mississippi Canyon to establish a baseline for ambient noise in the Gulf of Mexico against which to judge future noise impacts.

The Center for Marine Acoustic (CMA) Workbench will be a well-understood, respected, and dynamic tool for predicting acoustic and biological effects of anthropogenic sound on the outer continental shelf (OCS) — a “useful” model answering current needs, while driving next-generation regulatory approaches.  

BOEM’s High Level Approach: 

As regulatory requirements and technical capabilities change, BOEM’s underwater acoustic analysis and assessments must become both more complex and more flexible to meet changing demands. Without an in-house capability, BOEM is dependent on external modeling that cannot consistently provide the level of detail necessary for formal analysis in the required timeframe.  Additionally, while there are current models that approximate various phenomena and predict their effects elsewhere within specific parameters, there is no comprehensive model that meets BOEM’s long-term needs.  

BOEM needs: 

• An in-house capability to reliably estimate the effects of anthropogenic sound on marine life.   
• A capability that integrates various models, giving it the flexibility to develop new techniques and answer new questions as regulatory requirements and technical capabilities evolve. 
• Internal expertise to uses the Workbench to drive more complex questioning, interpret results, and contribute reliable quantitative assessments to recommendations for BOEM regulated activities. 
• The ability to provide formal and defensible analysis, as well as informal exploration by a variety of stakeholders and quality control oversight of contractors.   
• Recognition, both internally and outside of BOEM, as possessing legitimate and trusted expertise in the acoustic effects of all BOEM activities on the OCS.  

The CMA Workbench will answer these challenges through an integrated framework of models, tools, and analytic processes that yield results consistently recognized as high-quality by experts in the field.  Initially it will serve to BOEM managers and senior leaders needs, but it will expand to meet the needs of external stakeholders and customers.  The Workbench will be certified as part of an initial capabilities review, but it will also continuously grow and expanded in order to meet emergent scientific discoveries and regulatory requirements and perceived future needs.  This growth will expand the Workbench’s resolution of the details of the currently know acoustic effort but will also expand beyond acoustics and integrate with non-acoustic stressors.  It will be a tool to answer current questions, but also to formulate the next generation of questions. 

Passive Acoustic Monitoring (PAM) is a tool that is useful for observing the presence of vocalizing species, measuring the received levels of anthropogenic sound sources, and quantifying the levels and patterns of naturally occurring sounds. Many BOEM-funded studies over the years have utilized PAM, often alongside other monitoring methods such as visual observers or active acoustic sources (e.g., fish-finders).  Working with staff in our Office of Renewable Energy Programs, the Center for Marine Acoustics helped to host several workshops on using PAM in the Atlantic to observe populations of baleen whales. The workshop reports can be found at the links below.

During offshore wind development, BOEM anticipates that PAM will be employed for several purposes. Short-term recordings will measure sound levels from pile-driving operations. During the entire construction period, real-time PAM systems will be used to alert operators when protected species are nearby. For several years pre- and post-construction, archival PAM systems will help in assessing the presence of vocalizing marine mammals and fishes.

BOEM is working with several stakeholders to develop a vision for a long-term regional PAM network in the Atlantic Ocean. The benefit of a network, in which acoustic data are centralized and shared alongside other data streams, is that it allows for a more robust analysis and thus a greater understanding of where animals are, and ideally, some insights about what they are doing. The initial focus of this effort is to monitor populations of baleen whales, but additional species may be recorded and analyzed as well.

BOEM is working closely with the Regional Wildlife Science Collaborative to develop best practices for data collection, analysis, and sharing. In 2021, several BOEM staff co-authored a paper with colleagues at National Marine Fisheries Service outlining the general utility of PAM and proposing an initial framework for this regional PAM network.